1. Field of the Invention
This invention relates to a processing method for a substrate and a processing unit for a substrate.
2. Disclosure of the Prior Art
Processes for manufacturing semiconductor devices include steps in which semiconductors as substrates undergo processes such as oxidation, diffusion, CVD (Chemical Vapor Deposition) or the like. Thermal processing units are often used for conducting the various processes. A conventional thermal processing unit comprises: an operation area where an operator or an automatic conveying robot holds and conveys a carrier housing semiconductor wafers, and a loading area where semiconductor wafers in the carrier are transferred to a wafer-boat as a holder of substrates which is then loaded into or unloaded from a thermal processing furnace.
In such thermal processing units, it is preferable for a partition (bulkhead) to be provided between the operation area which is exposed to the atmosphere and the loading area. The partition allows the loading area to remain cleaner than the operation area and prevents a natural oxidation film from forming on the semiconductor wafers. The loading area should also be preferably filled with an inert gas such as nitrogen. A closed-type carrier, whose entrance for semiconductor wafers can be hermetically closed by a lid, should also be preferably used in the thermal processing unit in order to prevent the semiconductor wafers from being contaminated with particles.
An opening is provided in the partition between the operation area and the loading area. A door is provided at the opening to open and close it. When processing the semiconductor wafers, the lid of the carrier is aligned to be in contact with the opening, and the door and the lid are opened to communicate the interior of the carrier with the loading area. The semiconductor wafers are then conveyed from the interior of the carrier to the wafer-boat in the loading area via the opening. The wafer-boat is then loaded in the thermal processing furnace to perform the prescribed processes on the semiconductor wafers. The way of opening the door and the lid together is described in Japanese Patent Laid-Open No. 8-279546.
The interior of the carrier is full of the atmospheric air unless it is filled with another gas such as an inert gas. Because of this, the air in the carrier may flow into the loading area when the carrier is aligned with the opening and the door and the lid are opened. The concentration of the oxygen in the loading area increases if the air in the carrier flows into the loading area. This makes the replacement of the atmospheric air with an inert gas more time-consuming and increases the possibility of oxidation film forming on the semiconductor wafers. This may have a bad effect on processing.